The research on vital sign detection using noncontact Doppler radar has been carried out since the 1970's. Since then, many methods have been proposed to help to improve the measurement accuracy, lower the noise level and extend the detection range. A receiver with homodyne architecture has been applied to eliminate the detection null points by using both the in-phase and quadrature-phase (I/Q) output. The RF front end also effectively depressed the phase noise from VCO with range correlation effect.